The present invention relates to a process for preparing an urethane compound for medical instruments. More particularly, the present invention relates to a process for easily preparing an urethane compound (macromonomer) showing high safety, which is very useful for a material of medical instruments represented by optical materials such as a contact lens material and an intraocular lens material. Furthermore, the present invention relates to a process for preparing an urethane compound while molecular weight of the compound is controlled.
At present, various urethane compounds such as urethane foam, urethane rubber, adhesives and polyurethane synthetic fiber are industrially used.
In the absence of a catalyst or in the presence of a compound such as an organic metal compound or a tertiary amine, hydroxyl group is reacted with isocyanate group to form urethane bond. Particularly, from the viewpoint of high catalytic activity, the organic metal compounds are generally used. Among them, an organic tin compound is well known.
However, it is considered that the organic tin compound which is generally known as a compound showing high toxicity must not be used as a catalyst for preparation of urethane materials when the urethane materials are applied for medical instruments which are used in living organism or by contacting with living organism. The organic tin compound is recognized as a distraction substance for endocrine (environmental hormone) which is recently topical substance. Accordingly, some catalysts other than organic tin compounds are earnestly necessitated.
From the viewpoint of mechanical strength and excellent oxygen permeability, urethane bond-containing siloxane compounds (macromonomers) have been examined for the use as medical instruments, in particular, optical materials such as a contact lens material and an intraocular lens material (Japanese Unexamined Patent Publication No. 22487/1979, Japanese Unexamined Patent Publication No. 121826/1994, U.S. Pat. No. 5,451,617 and the like). However, because the siloxane compounds disclosed in these references are prepared by using the organic tin compounds almost, these siloxane compounds are not suitable as medical materials on the basis of the above reasons. Even if purification of the siloxane compound is carried out, the organic tin compounds remain within the siloxane compound.
Usually, the above urethane bond-containing siloxane compounds (macromonomers) have been prepared by finally introducing a polymerizing group in a polyfunctional polysiloxane which is a main chain through urethane bond (Japanese Unexamined Patent Publication No. 179217/1986, Japanese Unexamined Patent Publication No. 35014/1991 and the like). However, when this method is employed, it is inevitable that the polymerizing group is inestimably and repeatedly introduced in the polyfunctional polysiloxane which is a main chain through urethane bond. As a result, molecular weight of the obtained siloxane compound becomes higher than planned molecular weight. Accordingly, there is a problem that clear understanding for structure of the obtained compound is difficult.
Because the above siloxane compound becomes high viscous solution according to its molecular weight or kind of reaction components, effective purification methods for the siloxane compound are not developed. So, it is very difficult to remove impurities such as the above catalyst and by-products, and crude siloxane compound is used. Accordingly, the use of the siloxane compounds has been feared from the viewpoint of safety, including the above problems.
An object of the present invention is to provide a process for easily preparing an urethane compound, in particular, while molecular weight of the compound is controlled, in the absence of a catalyst or in the presence of a catalyst showing lower toxicity instead of the conventional organic tin compounds.
This and other objects of the present invention will become apparent from the description hereinafter.
In accordance with the present invention, there is provided a process for preparing an urethane compound for medical instruments, characterized by
reacting a hydroxyl compound (A) with an isocyanate compound (B) in the absence of a catalyst or in the presence of a reaction catalyst other than an organic tin compound to give an urethane compound (I).
According to the process of the present invention, an urethane compound showing high safety, which is very useful for a material of medical instruments represented by optical materials can be easily prepared, in particular, while molecular weight of the compound is controlled.